Household illuminating and heating kerosene has been known and used for since the late 1850's. Kerosene has a wide boiling range of 150-300° C. However, narrow boiling ranges are produced for improved control of final product combustion properties. Kerosene burning household appliances are manufactured with the specific characteristics of kerosene in mind. Known kerosene's are derived from crude oil by fractional distillation. Crude oil derived kerosene normally appears light yellow, contains sulphur, and aromatics which give the kerosene a distinct and negatively perceived odour.
Prior art processes for manufacturing illuminating and heating kerosene includes drying low sulphur paraffinic kerosene's to remove water and removing mercaptan by means of caustic washing or additional treatment to convert mercaptans to odorless disulphides. Highly paraffininic feed stocks may require additives to improve their performance in cold climates, these could include pour point depressants or wax crystal modifiers.
In the case of naphthenic or high sulphur crudes, processes for manufacturing illuminating and heating kerosene includes hydrotreating followed by acid treatment followed by water washing, or solvent extraction combined with caustic washing and clay treatment to remove undesirable aromatics and sulphur compounds. In the case of cracked feedstocks derived from heavy fuel oils, severe hydrotreating is required to remove olefins and other unstable compounds.
It is well known that aromatics are carcinogenic. When crude derived kerosene is burned it produces particulate matter, which leaves a residue. Residue needs to be cleaned from any household appliances. Crude derived kerosene also produces smoke and a distinct smell when it is burned. Due to the toxicity, appearance and odour of crude derived kerosene, it has not been widely accepted in modern households despite its relatively low cost. Recently however, synthetically derived kerosene appeared on the market. Synthetically derived kerosene is normally colourless and has preferred burning characteristics. Although it is more widely acceptable for household use than crude derived kerosene middle distillates, it contains aromatics. It is well known that aromatics are carcinogenic and gives the kerosene a distinct and still negatively perceived odour. An example of such known synthetically derived kerosene containing high levels of aromatics is a kerosene distillate cut from the High Temperature Fisher-Tropsch process. Household illuminating and heating kerosene contains three main types of paraffinic, naphthenic, and aromatic hydrocarbons. The quality of kerosene as a burning or heating oil is related to its burning characteristics and is dependent on such factors as its composition, volatility, viscosity, calorific value, sulphur content, and freedom from corrosive substances or contaminants.
It is an object of this invention to provide synthetically derived kerosene, which is colourless, odourless, non toxic, has excellent cold flow properties over a relatively wide boiling range while not giving away good flash point characteristics and having excellent burn characteristics.
The applicant is aware that, while paraffin's have excellent burning properties, aromatics, in particular multiple ring polynuclear aromatics, tend to burn less elegantly and contribute to smoke and carbon formation. Naphthenes have intermediate properties however, their combustion characteristics tend to be closer to paraffins than aromatic hydrocarbon types. In order to limit smoke formation, paraffinic feedstocks are selected for indoor illumination and heating purposes, and aromatic feedstocks especially those with multiple ring aromatics as well as cracked feedstocks containing olefins are avoided.
The applicant has found that the burn characteristics of kerosenes improve with in the presence of trace amounts of mono-aromatic species (single ring compounds only). The applicant has further found that too high levels of aromatics and naphtenes burn with a reddish and sometimes smoky flame. However, it is an object of this invention to provide a kerosene with negligible quantities of aromatics and comprising mainly of iso-paraffins.
In this specification, references to percentage proportions refer to mass percentage proportions. In this specification, general reference to burn characteristics, refers to burning characteristics in wick-fed yellow flame burners, which are not of the primus type however these fuels perform well in aspirated and high pressure atomising gun burners as well.